The present invention relates to code division multiple access (CDMA) signal analysis, and more particularly to a visualization of active codes, their spreading factors and power levels, in a code domain power display.
In a CDMA signal using orthogonal codes, all of which are the same length (the length being known as “spreading factor”), the amount of power present in each code, i.e., code domain power (CDP), is displayed by plotting the power in each code versus the code number index on a two-dimensional column graph. This is a conventional and well-understood manner using linear index code order for displaying CDP information. Newer CDMA systems, such as cdma2000, now specify use of codes of varying spreading factors, i.e., of different lengths, which complicates the display of CDP. Specifically codes of smaller spreading factor, when displayed in a CDP graph that is appropriate for the code having the largest spreading factor, appear dispersed into multiple sub-codes at fixed distances determined by their relationship to the larger spreading factor code system, e.g., a cdma2000 code with a spreading factor of 16 when displayed on the code graph for a spreading factor of 128 has 8 sub-codes spaced 8 indices apart. Spreading factor is not visually apparent for any of the codes.
U.S. Pat. No. 6,219,340 describes one method of displaying power levels for a CDMA signal having orthogonal codes with different spreading factors or code layers. In this display a power level for each active code channel is displayed using a vertical bar, with the width of the bar indicating in which code layer each active code channel is active. Each code is rendered with a color to indicate spreading factor, but this method does not give an intuitive sense for the information because the colors don't directly convey a sense of magnitude or ordering.
Co-pending U.S. patent application Ser. No. 09/919,690, filed Jul. 31, 2001, presents another display for CDP where the sub-codes are grouped together by plotting them in bit-reversed index code order, equivalent to transforming a Walsh code indexing scheme into an orthogonal variable spreading factor indexing scheme. This scheme also does not convey a sense of magnitude or ordering.
What is desired is a means of visually indicating both power and spreading factor for each code, or sub-code, in a graph of code domain power for code domain multiple access systems having multiple spreading factors.